Colour ink-jet printing method with optimized number of deposited droplets and corresponding printer

ABSTRACT

A a color ink-jet printer has at least four ink cartridges each containing one basic color selected from among yellow, magenta, cyan and black, and at least one additional cartridge containing a basic pale color ink. A processor receives a printing order containing data concerning the requested color and/or the number and color of the ink droplets to be deposited on one another at a specific location of a selected printing substrate. The processor includes an optimizing mode capable of matching the requested color and/or the required number and color of droplets to be superimposed to obtain a selected color at a given pixel with an equivalent color and/or an equivalent number and/or color of droplets to be superimposed to obtain a substantially equivalent and satisfactory color rendering in conformity with the human eye sensory response. The thus-determined equivalent color and/or the equivalent number and color of droplets to be superimposed is applied to the printer for each printing order received.

This disclosure is based upon French Application No. 02/14057, filedNov. 8, 2002, and International Application No. PCT/FR2003/003314, filedNov. 6, 2003, the contents of which are incorporated herein byreference.

The present invention concerns colour ink-jet printing using an ink-jetprinter comprising a plurality of cartridges each containing an ink tobe sprayed in the form of droplets onto a print medium.

It finds a general application in the optimisation of colour ink-jetprinting with a view to reducing the thickness of the ink deposit at agiven location, referred to as a pixel, and to reduce accordingly theconsumption of ink, without affecting the sensory response of the humaneye.

In general terms, ink-jet printers comprise four cartridges eachcontaining a basic or primary colour, namely yellow, magenta, cyan andblack.

In order to increase the final rendition of the image, in particular inphotography, some printers also comprise supplementary cartridgescontaining primary colour inks referred to as “pale”, such as palemagenta, pale cyan and pale black.

The use of a printer equipped with seven cartridges each containing oneof these seven colours makes it possible to resolve the lack ofresolution of ink-jet technology.

However, such a use of the seven colours gives rise to problems ofexcessive thickness of the ink droplets liable to be superimposed in apixel as well as high ink consumption.

The present invention affords a solution to these problems.

It relates to a printing method of a colour ink-jet printer of the typecomprising at least four ink cartridges each containing a basic colourchosen from amongst yellow, magenta, cyan and black and at least onesupplementary cartridge containing an ink of a basic so-called palecolour, and in which a print instruction is received containinginformation relating to the requested colour and/or to the number andcolour of the ink droplets to be superimposed required for obtaining therequested colour in a given pixel of a chosen print medium.

According to a general definition of the invention, the method comprisesan optimisation mode in which the requested colour and/or the requirednumber and colour of the droplets to be superimposed in order to obtainthe requested colour at the said pixel is made to correspond to anequivalent colour and/or an equivalent number and colour of the dropletsto be superimposed making it possible to obtain a substantiallyequivalent and satisfactory colour rendition in accordance with thesensory response of the human eye, and there are applied to the printerthe equivalent colour and/or the equivalent number and colour of thedroplets to be superimposed thus determined for each print instructionreceived.

Thus, by virtue of the method according to the invention, it ispossible, without altering the rendition of the printing for the humaneye, to reduce the quantity of superimposed droplets and thus to reducethe thickness and quantity of ink deposited in a given pixel.

According to a preferred embodiment of the invention, the equivalentnumber of droplets to be superimposed is less than the required numberof droplets to be superimposed, preferably less than or equal to four orthree droplets of ink of different colours when the printer is equippedwith at least six ink cartridges.

Preferably the optimisation mode comprises several corresponding levels.

Another object of the present invention is a colour ink-jet printer ableto implement the method according to the invention, the said printerbeing of the type comprising at least four cartridges each containing abasic colour chosen from amongst yellow, magenta, cyan and black and asupplementary cartridge containing a so-called pale basic colour ink,and processing means able to process a print instruction comprisinginformation relating to the requested colour and/or to the requirednumber and colour of the droplets of ink to be superimposed in order toobtain the requested colour in a given pixel of a chosen print medium.

According to another characteristic of the invention, the processingmeans are able to make the requested colour and/or the required numberand colour of droplets to be superimposed in order to obtain therequested colour at the said pixel to correspond to an equivalent colourand/or an equivalent number and colour of the droplets to besuperimposed making it possible to obtain a substantially equivalent andsatisfactory colour rendition in accordance with the sensory response ofthe human eye, and to apply to the printer the equivalent colour and/orthe equivalent number and colour of the droplets to be superimposed thusdetermined for each print instruction received.

In practice, the correspondence is established according to a law or apre-established table of correspondence.

Yet another object of the present invention is software intended todrive a colour ink-jet printer of the type comprising at least fourcartridges each containing a basic colour chosen from amongst yellow,magenta, cyan and black and a supplementary cartridge containing aso-called pale basic colour ink, the said software comprisinginstruction codes able to process a print instruction comprisinginformation relating to the colour requested and/or to the requirednumber and colour of the droplets of ink to be superimposed in order toobtain the requested colour in a given pixel of a chosen print medium.

According to another characteristic of the invention, the instructioncodes of the software are able to make the requested colour and/or thenumber and colour of the droplets to be superimposed required forobtaining the requested colour at the said pixel correspond to anequivalent colour and/or an equivalent number and colour of droplets tobe superimposed making it possible to obtain a substantially equivalentand satisfactory colour rendition in accordance with the sensoryresponse of the human eye, and to apply to the printer the equivalentcolour and/or the equivalent number and colour of the droplets to besuperimposed thus determined for each print instruction received.

Other characteristics and advantages of the invention will emerge in thelight of the following detailed description and the drawings, in which:

FIG. 1 depicts the stacking of six droplets of different colours withoutthe optimisation method according to the invention,

FIG. 2 depicts the stacking of three droplets of different colourshaving substantially the same rendition as the stacking in FIG. 1according to the optimisation method according to the invention;

FIG. 3 depicts schematically a curve illustrating a colour reproduced bythe stacking of the six droplets of FIG. 1 and a colour reproduced bythe stacking of the three droplets of FIG. 2 according to the methodaccording to the invention;

FIG. 4 depicts a table of correspondence according to the inventionbetween the requested colour and/or the number and colour of droplets tobe superimposed required for producing several chosen colours in a givenpixel on the one hand and an equivalent colour and/or an equivalentnumber and colour of the droplets to be superimposed making it possibleto obtain a substantially equivalent and satisfactory colour renditionaccording to the sensory response of the human eye on the other hand,and

FIG. 5 is a schematic view representing a printer able to implement thesteps of the optimisation method according to the invention.

The present invention adapts to any colour ink-jet printing method.

In practice, a colour ink-jet printer comprises four cartridges eachcontaining a colour chosen from amongst the four basic colours: yellowJ, magenta M, cyan C and black K.

In order to increase the final rendition of the image, it is known howto associate, with these four basic colour ink cartridges, supplementarycartridges containing pale colour inks such as pale magenta Mpale, palecyan Cpale and pale black Kpale.

For example, with reference to FIG. 1, a stacking E6 of six droplets ofink of different colours (here yellow J, pale magenta Mpale, black K,cyan C and magenta M) is produced as a given pixel of a given printmedium from a printer with seven cartridges.

Such a stacking E6 has a colour rendition with a wavelength of around560 nm (FIG. 3).

Surprisingly, the applicant found that a stacking E3 (FIG. 2) of threedroplets of ink of different colours (here magenta M, cyan C and blackK) has a colour rendition with a wavelength, here around 550 nm,substantially equivalent to that of the stacking E6, and that thespectral shift between the two colour renditions (here around 10 nm)does not affect the sensory response of the human eye, or only verylittle.

From this finding (obviously achieved under generally similar printing,environment and temperature conditions), the applicant established a lawor table of correspondence TAB (FIG. 4) between several requestedcolours and/or the number and colour of the droplets to be superimposedrequired for reproducing the said requested colours as a given pixel onthe one hand and equivalent colours and/or equivalent numbers andcolours of droplets to be superimposed making it possible to obtain asubstantially equivalent and satisfactory colour rendition in accordancewith the sensory response of the human eye on the other hand.

For example, to the requested colour CD5, there is allocated therequested stacking ED5 formed by:

an ink droplet of colour Xx chosen from amongst the seven cartridges,

a black ink droplet K,

a pale black ink droplet Kpale,

a cyan ink droplet C,

a pale cyan ink droplet Cpale,

a magenta ink droplet M, and

a pale magenta ink droplet Mpale.

According to the invention, without substantially affecting the responseof the human eye, the requested colour CD5 and/or the stacking ED5 arereplaced by the equivalent colour CE5 and/or the equivalent stacking EE5formed by

an ink droplet of colour Xx,

an ink droplet of colour black K,

an ink droplet of magenta M, and

an ink droplet of cyan colour C.

The method according to the invention thus makes it possible to obtain areduction G5 of three droplets of ink.

Naturally, other correspondences can be established between therequested colours and the equivalent colours as well as between thenumber and colour of the required droplets and the number and colour ofthe equivalent droplets.

In practice, the law or table of correspondence TAB is established inadvance before executing the method of optimising the deposition of ink.

The optimisation method can also comprise several correspondence levels,for example fine, coarse or normal. To each level there is allocated athreshold whose value corresponds to a spectral shift (expressed in nm)between the requested colour and the equivalent colour. For example, thespectral shift corresponding to the coarse level is greater than 20 nmwhilst the spectral shift of the fine level is less than 10 nm.

The applicant obtained a saving of around 25% on the quantity of inkused to print logos on chip cards with a droplet volume of around 18picolitres and an average volume per face of around 60 microlitres withthe optimisation method according to the invention.

With reference to FIG. 5, the implementation of the optimisation methodis shown in a colour ink-jet printer such as the one sold by the companyEPSON under the reference Stylus series PHOTO 850, 890, 950.

The colour ink-jet printer 1 comprises for example six to eightcartridges 2, four cartridges of which each contain a colour chosen fromamongst the four basic colours, yellow J, magenta M, cyan C and black Kand two, three or four cartridges of which contain inks of pale colourchosen from amongst pale magenta Mpale, pale cyan Cpale and pale blackKpale.

Conventionally, a controller or driver 3 for the printer 1 receives aprint instruction 4 comprising information relating to the request for acolour CC and/or to the number and colour of the ink droplets G to besuperimposed in order to reproduce a chosen colour at a given location,referred to as the pixel Pi, on a chosen print medium 5.

For example, the instruction 4 emanates from an image processor (notshown) of the RIP type, standing for “Raster image processor” residentin a distant computer (not shown) containing the digital image to beprinted. In a variant, the RIP processor resides in the printer 1.

The controller 3 consults, via the connection 6, a memory 7 containing atable TAB or law of correspondence between the requested colour and/orthe required number and colour of the droplets to be superimposed ED inorder to reproduce at least one colour chosen as a given pixel on theone hand and an equivalent colour CE and/or an equivalent number andcolour of droplets to be superimposed EE making it possible to obtain asubstantially equivalent and satisfactory colour rendition in accordancewith the sensory response of the human eye on the other hand.

In a variant, the correspondence is established by software whoseinstruction codes are executed by the controller 3 or anothermicroprocessor (not shown). The instruction codes of the software arecontained in a memory medium (not shown).

The controller 3 actuates the print head (not shown) containing the inkcartridges 2 according to the equivalent colour CE and/or the equivalentnumber and colour of the droplets to be superimposed EE thus determinedfor each requested colour CD and/or for each requested stacking ED.

The print head thus actuated brings the ink from the ink cartridges 2 tothe nozzles (not shown) of the print head of the printer with the viewto being expelled in the form of droplets G in accordance with theequivalent colour CE and/or the equivalent number and colour of thedroplets to be superimposed EE thus determined.

1. A method for printing with a color ink-jet printer having at leastfour ink cartridges respectively containing basic colors and at leastone supplementary cartridge containing an ink of a pale color, wherein arequested color can comprise a plurality of component colors selectedfrom said basic colors and said pale color, and the printing of arequested color is performed by depositing a drop of ink for each ofsaid component colors, superimposed upon one another, said methodcomprising the following steps: for each of a plurality of requestablecolors, establishing an equivalent color having a smaller amount ofcomponents than the requestable color; storing said equivalent colors inassociation with the corresponding requestable colors; in response to arequest to print a color at a location for a given pixel, retrieving thestored equivalent color for the requested color; and depositing a dropof ink for each component of the retrieved equivalent color at saidlocation, to thereby print said equivalent color in place of therequested color for said pixel.
 2. The method of claim 1, wherein theprinter has a plurality of supplementary cartridges, and said palecolors are selected from the group consisting of pale magenta, pale cyanand pale black.
 3. The method of claim 1, wherein said equivalent colorsare stored in the form of a table.
 4. The method of claim 1, wherein anequivalent color has a wavelength that Is sufficlently close to Itscorresponding requestable color so as to present substantially the samesensory perception to a humen observer.
 5. The method of claim 4,wherein the difference is wavelength between the requestable andequivalent colors is no greater than 20 nm.
 6. The method of claim 1,wherein, for each of at least some of said requestable colors, aplurally of equivalent colors are established for different respectivelevels of correspondence.
 7. The method of claim 6, wherein saiddifferent levels of correspondence are respectively associated withdifferent ranges of wavelength difference between the requestable colorand the equivalent color.
 8. A color ink-jet printer comprising: atleast four ink cartridges respectively containing basic colors and atleast one supplementary cartridge containing an ink of a pale color,wherein a requested color can comprise a plurality of component colorsselected from said basic colors and said pale color; a memory storing,for each of a plurality of requestable colors, an equivalent colorhaving a smaller amount of components than the requestable color; and acontroller that responds to a request to print a color at a location fora given pixel by retrieving the stored equivalent color for therequested color from said memory, and causing said printer to deposit adrop of ink for each component of the retrieved equivalent color at saidlocation, to thereby print said equivalent color in place of therequested color for said pixel.
 9. The printer of claim 8, comprising aplurality of supplementary cartridges, wherein said pale colors areselected from the group consisting of pale magenta, pale cyan and paleblack.
 10. The printer of claim 8, wherein said equivalent colors arestored in said memory in the form of a table.
 11. The printer of claim8, wherein, for each of at least some of said requestable colors, aplurality of equivalent colors are stored for different respectivelevels of correspondence.
 12. The printer of claim 11, wherein saiddifferent levels of correspondence are respectively associated withdifferent ranges of wavelength difference between the requestable colorand the equivalent color.